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Test Your Knowledge in Computers #582
Difficulty: Medium
A buffered input or output stream is one in which data that is read or written is actually stored in memory in a buffer until such a time as the buffer is flushed and the accumulated data is passed to or from the actual file.
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badsect(8) [bsd man page]

BADSECT(8)						      System Manager's Manual							BADSECT(8)

NAME
badsect - create files to contain bad sectors SYNOPSIS
/sbin/badsect sector ... DESCRIPTION
Badsect makes a file to contain a bad sector. Normally, bad sectors are made inaccessible by the standard formatter, which provides a for- warding table for bad sectors to the driver; see bad144(8) for details. If a driver supports the bad blocking standard it is much prefer- able to use that method to isolate bad blocks, since the bad block forwarding makes the pack appear perfect, and such packs can then be copied with dd(1). The technique used by this program is also less general than bad block forwarding, as badsect can't make amends for bad blocks in the i-list of file systems or in swap areas. Adding a sector which is suddenly bad to the bad sector table currently requires the running of the standard DEC formatter, as UNIX does not supply formatters. Thus to deal with a newly bad block or on disks where the drivers do not support the bad-blocking standard badsect may be used to good effect. Badsect is used on a quiet file system in the following way: First mount the file system, and change to its root directory. Make a direc- tory BAD there and change into it. Run badsect giving as argument all the bad sectors you wish to add. (The sector numbers should be given as physical disk sectors relative to the beginning of the file system, exactly as the system reports the sector numbers in its con- sole error messages.) Then change back to the root directory, unmount the file system and run fsck(8) on the file system. The bad sectors should show up in two files or in the bad sector files and the free list. Have fsck remove files containing the offending bad sectors, but do not have it remove the BAD/nnnnn files. This will leave the bad sectors in only the BAD files. Badsect works by giving the specified sector numbers in a mknod(2) system call (after taking into account the filesystem's block size), creating a regular file whose first block address is the block containing bad sector and whose name is the bad sector number. The file has 0 length, but the check programs will still consider it to contain the block containing the sector. This has the pleasant effect that the sector is completely inaccessible to the containing file system since it is not available by accessing the file. SEE ALSO
mknod(2), bad144(8), fsck(8) BUGS
If both sectors which comprise a (1024 byte) disk block are bad, you should specify only one of them to badsect, as the blocks in the bad sector files actually cover both (bad) disk sectors. On the PDP-11, only sector number less than 131072 may be specified on 1024-byte block filesystems, 65536 on 512-byte block filesystems. This is because only a short int is passed to the system from mknod. 3rd Berkeley Distribution BADSECT(8)

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badsect(8)						      System Manager's Manual							badsect(8)

NAME
badsect - Creates files to contain bad sectors SYNOPSIS
/usr/sbin/badsect bbdir sector... DESCRIPTION
The badsect command makes a file to contain a bad sector. Normally, bad sectors are made inaccessible by the standard formatter, which provides a forwarding table for bad sectors to the driver. If a driver supports the bad blocking standard, it is preferable to use that method to isolate bad blocks because the bad block forwarding makes the disk appear perfect, and such disks can then be copied with dd(1). The technique used by badsect is also less general than bad block forwarding, as badsect cannot make amends for bad blocks in the i-list of file systems or in swap areas. On some disks, adding a sector that is suddenly bad to the bad sector table currently requires the running of the standard formatter. Thus, to deal with a newly bad block or on disks where the drivers do not support the bad-blocking standard, badsect can be used to good effect. Use the badsect command on a quiet file system in the following way: Mount the file system and change to its root directory. Make a direc- tory BAD there. Run badsect, giving as argument the BAD directory followed by all the bad sectors you wish to add. (The sector numbers must be relative to the beginning of the file system, as reported in console error messages.) Change back to the root directory, unmount the file system, and run fsck(8) on the file system. The bad sectors should show up in two files or in the bad sector files and the free list. Have fsck remove files containing the offending bad sectors, but do not have it remove the BAD/nnnnn files. This operation will leave the bad sectors in only the BAD files. The badsect command works by giving the specified sector numbers in a mknod(2) system call, creating an illegal file whose first block address is the block containing bad sector and whose name is the bad sector number. When fsck discovers the file, it will ask "HOLD BAD BLOCK?" An affirmative response will cause fsck to convert the inode to a regular file containing the bad block. RESTRICTIONS
If more than one of the sectors comprised by a file system fragment are bad, you should specify only one to badsect, as the blocks in the bad sector files cover all the sectors in a file system fragment. ERRORS
The badsect command refuses to attach a block that resides in a critical area or is out of range of the file system. A warning is issued if the block is already in use. SEE ALSO
Commands: fsck(8) badsect(8)

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